This invention relates to the manufacture of dielectric substrates, particularly multilayer substrates, which include electrically conductive, semi-conductive, resistive, or capacitive elements such as pads, pins, or vias, which substrates may then be used in a computer component.
In the fabrication of high performance computer hardware, it is known practice to attach semiconductor chips to ceramic or plastic chip carriers which contain wiring elements interconnecting individual chips mounted on the same carrier and which contain provisions for electrically connecting the chips to external devices. It is also known practice to fabricate carriers having more than one layer, described variously in the art as multilayer carriers, multilayer modules, multilayer substrates, or multilevel substrates, hereafter referred to as multilayer substrates. Such multilayer substrates consist of one or more layers or sheets of a dielectric material which form insulating levels together with alternating layers consisting of individual co-planar, or essentially co-planar, conducting elements which form circuit pattern levels. A preferred feature of a multilayer substrate is a means for interconnecting the individual co-planar conducting elements from one side of a given insulating layer with the conducting elements on the opposite side of the same insulating layer by passing directly through the insulating layer so as to form a complete circuit path from one circuit pattern level to another circuit pattern level. Such an interconnecting conducting element, also known as a via, allows for the crossing of one conductor over another conductor where the insulating level is interposed, thus providing for a greater number of possible independent circuit paths and also for increased circuit density.
There are several methods for fabricating the interconnecting conducting elements which pass through the insulating layer. These fabrication methods include lithographic processes similar to those used for semiconductor chip fabrication, and mechanical processes which include the steps of punching holes in the insulating layer and then adding material to form conductive structures passing through the holes. Methods for adding such material may include the filling of the holes with metallic pastes or the insertion of metal pins or similar structures. Of the several methods, mechanical processes are preferred because of cost.
One method of forming and transferring electrically conductive elements is shown in U.S. Pat. No. 2,854,074. This patent discloses a method of punching a conductive sheet and transferring the formed conductive element into a conductive substrate so as to displace a portion of the conductive substrate material. One disadvantage of the method as applied to the fabrication of multilayer substrates is the requirement for a die member which must be interposed between the conductive sheet and the conductive substrate.
A method of forming and transferring electrically conductive elements into an insulator is shown in U.S. Pat. No. 4,897,919. This patent discloses a method of forming an electrically conductive element by punching a conductive sheet and transferring the formed conductive element into an aperture in an insulator. A related method of forming and transferring electrically conductive elements into an insulator is shown in U.S. Pat. No. 5,035,049. This patent discloses a method of forming an electrically conductive element by punching a conductive sheet and transferring the formed conductive element onto, but not through, an insulator. A similar method is disclosed in German Patent DT 2,734,461 wherein a plurality of electrically conductive elements are formed by punching a conductive sheet and simultaneously transferring the formed conductive elements into previously formed perforations in an insulator. As in the previous art, one disadvantage of each method as applied to the fabrication of multilayer substrates is the requirement that a die member be interposed between the conductive sheet and the insulator.
The present invention is a method of forming and transferring electrically conductive, semi-conductive, resistive, or capacitive elements from a sheet of conducting material or a sheet of conductive, semi-conductive, resistive, or capacitive elements into a deformable dielectric material. If desired, a plurality of sheets of deformable dielectric material with the conductive elements therein may be stacked to form a multilayer substrate. The sheet of conducting material or the substrate may also be perforated or partially perforated. The sheet of conducting material may include sheets which comprise a clad or a porous material. The dielectric material may be perforated, partially perforated, or not perforated. The method comprises the steps of providing a multilayer structure comprising a sheet of a conducting material which is in direct contact with a sheet of a deformable dielectric material, followed by the use of a punch or similar element to form one or more slugs from the sheet of conducting material and then to immediately transfer the slug into the dielectric material. In one preferred embodiment of the invention, the method may include the additional step of displacing a portion of the deformable dielectric material so as to cause an interference fit between the slug and the dielectric material. In another preferred embodiment, the method may include, in addition or alternatively to other preferred embodiments, the step of aligning the punch or the multilayer structure with respect to the other. In yet another preferred embodiment, the method may also include the use of a porous conducting material to form the slug, which may be advantageous in the subsequent formation of metallurgical connections to the porous slug. Furthermore, the method may include the use of a clad conducting material to form the slug so as to cause a clad slug to be transferred. Articles produced by the method described herein may optionally have a means for electrically connecting to semiconductor chips attached thereto, or for electrically connecting to external devices.
Accordingly, one intended use of the present invention is as an improved method for the forming and transferring of one or more electrically conductive, semi-conductive, resistive, or capacitive elements into a deformable dielectric material which is useful in the fabrication of multilayer substrates for mounting semiconductor chips, where the improved method has the advantages of manufacturing process simplicity and reduced cost. In addition, the present invention may be useful in manufacturing or processing a variety of substrates, which may include, without limitation, sheets, moldings, castings, composite structures, integrated circuits, semiconductor chips, interconnect devices, multilayer chip carriers, circuit boards, component parts of thermal conduction modules, and other electronic substrates, and which may be perforated, partially perforated, or not perforated. Other advantages of the present invention are that the method may be useful for fabricating parts at a high rate, or that the method may be useful for fabricating parts having high circuit densities, or that the method may be useful for fabricating parts having precisely located conductors.
Additional uses and advantages of the present invention will become apparent to the skilled artisan upon reading the following detailed description of the invention and the preferred embodiments, considered in conjunction with the accompanying drawings.